save a picture, should be true .bmp file (not just .ext)
you can't change the name, only background.bmp allowed.

http://www.uvnc.com:8080/docs/uvnc-server.htmlBlankMonitorEnabled=1
This allow the viewer to blank the screen
CaptureAlphaBlending=1
Capture alphaBlending is needed for semi transparent windows
( xp, vista...) but use more cpu.
BlackAlphaBlending=0
Instead of using the powermanager to blank the monitor we put
a layered window on top and capture the windows below. Using
this option you also can define a custom blank by placing a file
"background.bmp" in the ultravnc folder.

if you use mirror driver, no effect, background.bmp is simply ignored.
hope would be fixed and should be allowed back to 1.0.9.5.1